Method for manufacturing digital micro-mirror device (DMD)

ABSTRACT

A method for manufacturing a semiconductor package is disclosed. A wafer including a plurality of semiconductor chips is provided. Each chip has one or more mirrors mounted thereon. Further, a plurality of bond pads formed on a periphery of the chip. Next, a photoresist is formed over the one or more mirrors. Then, the semiconductor chips are singulated from the wafer. One ore more semiconductor chips are mounted on a base substrate. The bond pads of the semiconductor chip are electrically connected with the base substrate. The photoresist is then removed from the semiconductor chips.

[0001] This application is a divisional of U.S. patent application Ser.No. 09/847,620 filed on May 2, 2001, now pending, which is hereinincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method for manufacturingsemiconductor device packages, and more particularly to a method formanufacturing digital micro-mirror device (DMD) packages.

[0004] 2. Description of the Related Arts

[0005] In order to keep pace with the development of personal computers,a display has been developed from a cathode-ray tube type display into aliquid crystal display or a mirror type display. Especially, with theincreasing demand for digital broadcasting appliances, a digital lightprocessing (DLP) technology for high resolution becomes more and moreimportant. A DMD, which is an essential component for the DLPtechnology, requires significant expertise in the manufacturing processfor mirrors so that high reliability and low cost in the manufacturingprocess can be obtained.

[0006] The DMD process involves driving the mirrors, and thus the properdriving of mirrors is very important. Further, moisture and dust withinthe packages affect the picture quality or resolution of the DMD as wellas its reliability or durability. Therefore, during the fabrication ofthe DMD packages, the DMD packages themselves need to be protected frommoisture and dust.

[0007]FIG. 1 is a plan view showing a conventional semiconductor chip 12for the DMD, and FIG. 2 is a cross-sectional view showing a DMD package100 containing the semiconductor chip 12 of FIG. 1. With reference toFIG. 1 and FIG. 2, the semiconductor chip 12 is attached to an uppersurface 21 of a base substrate 20 by interposing an Ag-epoxy adhesive 30therebetween. The semiconductor chip 12 and the base substrate 20 areelectrically interconnected to each other with one or more bonding wires40. In order to protect the semiconductor chip 12 from externalenvironmental stresses, a metal sealing ring 24 with a predeterminedheight is provided at the periphery of the upper surface 21 of the basesubstrate 20.

[0008] The components, including the semiconductor chip 12, arehermetically sealed up with a window lid 50. A heat sink stud 60 isattached to the lower surface 23 of the base substrate 20. The windowlid 50 comprises a metal lid frame 52 contacting the metal sealing ring24, and a window 54. A reflectance coating film 56 is applied to thelower surface of the window 54 along the periphery thereof. The metalsealing ring 24 and the base substrate 20 form a cavity 29, and amoisture getter (absorbent) 58 is attached to the lower surface of themetal lid frame 52 of the window lid 50 within the cavity 29. Externalterminals (not shown) are formed on the lower surface 23 of the basesubstrate 20.

[0009] A plurality of mirrors 16 (only a typical one of which isdepicted in FIG. 2) are formed on the active surface of thesemiconductor chip 12 at the center thereof, and one or more electrodepads 14 are formed on the active surface at the periphery thereof forinterconnection via the one or more bonding wires 40.

[0010]FIG. 3 is a flow chart 90 describing a manufacturing process ofthe conventional DMD package 100. Each step of the manufacturing processis described briefly below.

[0011] A wafer comprising a plurality of the semiconductor chips 12 isprepared (step 71). Herein, a photoresist film is formed on the uppersurface of the wafer in the predetermined portion. The photoresist filmprevents damage to the mirrors 16 from the external environment bycovering the mirrors 16. The photoresist film is not formed on theelectrode pads 14.

[0012] Prior to wafer-breaking, the wafer is half-cut (step 72). Thephotoresist film on the upper surface of the wafer is removed (step 73),and to shield the mirrors 16 from dust or moisture, a firstanti-sticking film is formed thereon (step 74). The wafer is broken andseparated into individual semiconductor chips 12 (step 75). A breakingmeans in a dome shape is brought into contact with to the back surfaceof the wafer and urged upwardly. As a result, the half-cut wafer isbroken into a plurality of individual semiconductor chips 12.

[0013] In the wafer-breaking step, silicon particle scraps aregenerated. Therefore, the silicon particles are removed (step 76).

[0014] The semiconductor chip 12 is attached to the upper surface 21 ofthe base substrate 20 by the Ag-epoxy adhesive 30 (step 77), and theAg-epoxy adhesive 30 is cured (step 78). The semiconductor chip 12 iselectrically interconnected to the base substrate 20 with the bondingwires 40 (step 79).

[0015] The organic compounds remaining on the upper surface 21 of thebase substrate 20, the semiconductor chip 12 on the surface 21, and thebonding wires 40 are removed (step 80). A second anti-sticking film isformed thereon (step 81).

[0016] The metal sealing ring 24 is mounted on the upper surface 21 ofthe base substrate 20, and the components are hermetically sealed by thewindow lid 50 having the moisture getter 58 attached thereon (step 82).

[0017] The heat sink stud 60 is attached to the lower surface 23 of thebase substrate 20 (step 83). The DMD package 100 is thus complete.

[0018] The above-described method for manufacturing the conventional DMDpackages has several problems as follows;

[0019] The manufacturing process is very complicated. The major reasonis that the manufacturing process for the conventional DMD packageemploys the wafer-breaking method for separating the wafer intoindividual semiconductor chips 12. Since the wafer-breaking methodcomprises a first step of half-cutting the wafer and a second step ofbreaking the wafer, compared to the full-cutting method, whichcompletely cuts the wafer at once, this method further involves anadditional step, i.e. the wafer-breaking step.

[0020] Even if the full-cutting method is employed to prevent thisdrawback, another problem occurs in the step of removing the photoresistafter separating the wafer into the semiconductor chips by thefull-cutting method. Conventionally, the wafer comprising separatedsemiconductor chips has the adhesive tape on its back surface. In thephotoresist-removing step after the wafer-cutting step, the adhesivefrom the adhesive tape and the photoresist are unnecessarily removedtogether. Thus, the individual semiconductor chips can be undesirablydetached from the adhesive tape. Therefore, the conventionalmanufacturing process normally cannot employ the full-cutting method.

[0021] The mirrors within the semiconductor chip 12 can be easilydamaged by the silicon particles generated in the wafer-breaking step.The silicon particles positioned between the mirrors 16 cannot beproperly removed by the washing step. Since the wafer-breaking step iscarried out after the step of removing the photoresist, damage to themirrors 16 by the silicon particles commonly occurs.

[0022] Since the Ag-epoxy adhesive is used to attach the semiconductorchip 12 to the base substrate 20, moisture enters the package due to thehygroscopicity of the Ag-epoxy. Further, an exhaust gas generated duringthe curing of the Ag-epoxy adhesive contaminates the mirrors 16 on theactive surface of the semiconductor chip 12. Therefore, it is preferableto use solder as the adhesive means. However, with the use of thesolder, damage such as the burning of the first anti-sticking film orthe deformation of the mirrors can occur. In other words, to attach thesemiconductor chip to the base substrate, the solder must be melted at atemperature of 150° C. or more. Such a high temperature causes theburning of the first anti-sticking film or the deformation of themirrors 16 in the semiconductor chip 12.

SUMMARY OF THE INVENTION

[0023] Accordingly, an object of the present invention is to simplifythe manufacturing process of the DMD packages.

[0024] Another object of the present invention is to prevent failuresgenerated in the sequence of steps including first half-cutting andsecond full-cutting the wafer. Still another object of the presentinvention is to prevent failures due to the use of the Ag-epoxyadhesive.

[0025] In order to achieve the foregoing and other objects, a method formanufacturing digital micro-mirror device (DMD) packages comprisespreparing a wafer including a plurality of DMD semiconductor chips, eachchip having a plurality of mirrors formed on the center of an activesurface, a plurality of electrode pads formed on the edges of the activesurface, and a photoresist for protecting the mirrors. The methodfurther comprises forming a metallic layer on a back surface of thewafer, said metallic layer being made of a metal having a low meltingpoint. It further comprises separating the wafer into the individualsemiconductor chips. It also comprises attaching each semiconductor chipto an upper surface of a base substrate with an adhesive made of a metalhaving a low melting point. The method then comprises the steps ofinterconnecting the electrode pads of the semiconductor chip to the basesubstrate with a bonding wire, removing the photoresist from thesemiconductor chips, and forming an anti-sticking film on the activesurface of the semiconductor chip for protecting the semiconductor chipsfrom dust and moisture. Finally, the method comprises hermeticallysealing the semiconductor chip and the bonding wires on the uppersurface of the base substrate by using a window lid.

[0026] It is preferable that the metallic layer is made of a metalhaving a low melting point selected from the group consisting of Va, Au,Ni, Ag, Cu, Al, Pb, Sn, Sb, Pd and metallic compounds thereof.

[0027] The step of forming a metallic layer comprises lapping the backsurface of the wafer and forming on the back surface a metallic layermade of a metal having a low melting point.

[0028] Solder is preferably used as the metal adhesive having a lowmelting point.

[0029] After the step of hermetically sealing the semiconductor chip andthe bonding wires, the manufacturing method of the DMD packages furthercomprises attaching a heat sink stud to the lower surface of the basesubstrate. Further, it is preferable that the step of hermeticallysealing the semiconductor chip and the bonding wires is carried out at atemperature which is no higher than the temperature of the step ofattaching the semiconductor chip to the base substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The various features and advantages of the present invention willbe readily understood with reference to the following detaileddescription taken in conjunction with the accompanying drawings, whereinlike reference numerals designate like structural elements, and, inwhich:

[0031]FIG. 1 is a schematic plan view showing a conventionalsemiconductor chip for digital micro-mirror device (DMD);

[0032]FIG. 2 is a cross-sectional view showing a conventional DMDpackage containing the semiconductor chip of FIG. 1;

[0033]FIG. 3 is a flowchart describing a conventional manufacturingprocess of the DMD package in FIG. 2;

[0034]FIG. 4 is a cross-sectional view showing a DMD package inaccordance with an embodiment of the present invention;

[0035]FIG. 5 is a flow chart describing a manufacturing process of theDMD package in FIG. 4;

[0036] FIGS. 6 through FIG. 16 illustrate schematically each step of themanufacturing process in FIG. 5; wherein FIG. 6 is a schematic plan viewthat illustrates a wafer used in the DMD packages; FIG. 7 is a plan viewthat illustrates the manufactured wafer;

[0037]FIG. 8 is a cross-sectional view taken along the line 8-8 in FIG.7;

[0038]FIG. 9 is a partial cross-sectional view showing back-lapping thewafer;

[0039]FIG. 10 is a cross-sectional view that illustrates forming a metallayer on the back surface of the wafer;

[0040]FIG. 11 is a cross-sectional view that illustrates cutting thewafer into individual semiconductor chip;

[0041]FIG. 12 is a cross-sectional view that illustrates attaching asemiconductor chip to a base substrate;

[0042]FIG. 13 is a cross-sectional view that illustrates wire-bonding;

[0043]FIG. 14 is a cross-sectional view that illustrates removing thephotoresist;

[0044]FIG. 15 is a cross-sectional view that illustrates hermeticallysealing the package with a window lid; and

[0045]FIG. 16 is a cross-sectional view that illustrates attaching aheat sink stud on the lower surface of the base substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] Preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings.

[0047]FIG. 4 is a cross-sectional view showing a DMD package 200 inaccordance with an embodiment of the present invention. With referenceto FIG. 4, a semiconductor chip 112 is attached to an upper surface 121of a base substrate 120 with a metallic adhesive 130 having a lowmelting point, and a metallic layer 115 made of a metal having a lowmelting point is formed on the back surface of the semiconductor chip112. The base substrate is preferably a ceramic board, a plastic board,or a printed circuit board. Herein, the metallic layer 115 enables themetallic adhesive 130 to be firmly attached to the semiconductor chip112. Other components are the same as those of the conventional DMDpackage 100 of FIG. 1. Referring to FIGS. 5 through 16, a manufacturingprocess of the DMD packages in accordance with an embodiment of thepresent invention is described below.

[0048]FIG. 5 is a flow chart 190 illustrating a manufacturing process ofthe DMD package 200 in FIG. 4. FIGS. 6 through 16 show each step of themanufacturing process of FIG. 5.

[0049] As shown in FIGS. 6 through 8, the manufacturing process startswith preparing the wafer 110 (step 191). The silicon wafer 110 comprisesa plurality of mirror-driving integrated circuits (not shown) formed byconventional techniques. A plurality of semiconductor chips 112 isformed on the wafer 110. Scribe lines 118 are also formed between theneighboring semiconductor chips 112, where the circuits are not formed.

[0050] The photoresist 113 is formed on a predetermined portion of theupper surface 10 a of the wafer 110. The photoresist 113 prevents damageto the mirrors 116 from the external environment. The photoresist 113 isnot formed on the electrode pads 114.

[0051] A metallic layer 115 is formed on the back surface 110 b of thewafer (step 192). The metallic layer 115 enables the metallic adhesiveto be firmly attached to the back surface 110 b of the wafer 110. Asshown in FIG. 9, the back surface 110 b is lapped with a lapping device180. Because the silicon oxide layer is naturally formed on the backsurface of the wafer 110, if the metallic layer is formed on the backsurface of the wafer 110 without any treatment, adhesion between theback surface of the wafer 110 and the metallic layer 115 can beundesirably weak.

[0052] For this reason, in this embodiment, the back surface 110 b islapped with the lapping device 180. However, the back surface may belapped by any suitable conventional etching techniques. As shown in FIG.10, the metallic layer 115 is formed on the lapped back surface 110 b ofthe wafer 110. With respect to the adhesive means and the temperature inthe chip attachment process, it is preferable to use a metal having alow melting point as the metallic layer 115. For example, the metal canbe Va (Vanadium), Au (Gold), Ni (Nickel), Ag (Silver), Cu (Copper), Al(Aluminum), Pb (Lead), Sn (Tin), Sb (Stibium), Pd (Palladium) andmetal-containing compounds thereof. Of course, the present invention isnot limited to such metals and compounds. Those of ordinary skill in theart should also be aware the other suitable metals or metallic compoundsare well within the broad scope of the present invention.

[0053] As shown in FIG. 11, the wafer 110 is separated into individualsemiconductor chips 112 by the full-cutting method (step 193). A scribeblade 170 saws the wafer 110 along the scribe lines 118 and therebyseparates the wafer 110 into individual semiconductor chips 112. Thiswafer-sawing step is carried out with the wafer 110 having the adhesivetape (not shown) attached to the back surface 10 b of the wafer 110.Then, the wafer-washing step is performed.

[0054] Since the mirrors 116 of the semiconductor chips 112 are coatedwith the photoresist 113, damage to the mirrors 116 by contaminants suchas silicon particles during the wafer sawing process can be prevented.

[0055] Conventionally, a step of removing the photoresist normallyfollows the washing step. However, with the conventional method, adelamination problem of the semiconductor chip from the adhesive tapeoccurs. In order to prevent this problem, in accordance with theembodiment of the present invention, as shown in FIG. 12, a chipattachment step (step 194) is followed. Each of the semiconductor chips112 is separated from the wafer (110 in FIG. 11), and attached to theupper surface 121 of the base substrate 120 by interposing an adhesive130 having a low melting point such as solder therebetween. Herein, theadhesive 130 is solidified at room temperature, and therefore the curingstep for the Ag-epoxy adhesive is omitted. Since a metallic layer 115 isformed on the back surface of the semiconductor chip 112, the adhesive130 is more firmly attached to the semiconductor chip 112. The adhesive130 can be provided in various forms such as a ribbon, paste, wire orany other suitable patterns.

[0056] If the adhesive 130 is used, the die-attaching step is carriedout at higher temperature than if the Ag-epoxy adhesive is used. Forexample, with the solder, the die attaching step is processed at atemperature of approximately 150° C. or more. However, since the mirrors116 of the semiconductor chip are coated with the photoresist 113,although the die-attaching step is carried out at a high temperature,the mirrors 116 of the semiconductor chips are not damaged.

[0057] Although this embodiment uses the base substrate 120 having aflat upper surface, other base substrates having a dented upper surfacemay be used. For the base substrate, however, a ceramic substrate havinglow hygroscopicity and high thermal conductivity preferably is used,although other plastic substrates or a printed circuit board may beused.

[0058] As shown in FIG. 13, the wire-bonding step is carried out (step195). Herein, the ball-bonding method using an Au bonding wire or thewedge-bonding method using an Al bonding wire may be alternativelyemployed. FIG. 13 shows the wedge-bonding method between the electrodepads 114 of the semiconductor chip 112 and the base substrate 120.

[0059] As shown in FIG. 14, the photoresist (113 in FIG. 13) is removed(step 196), and an anti-sticking film is formed (step 197). Thephotoresist 113 is not removed until after the wire-bonding step. Thisprevents the contamination of the mirrors 116 due to dust or moisture.However, after the wire-bonding step, the photoresist 113 on the mirrors116 is removed, because the mirrors 116 in the semiconductor chip 112are protected from the outside when sealing the components including thesemiconductor chip with the window lid. Then, the anti-sticking film forpreventing the sticking of dust or moisture is formed.

[0060] The photoresist 113 is removed from the semiconductor chip 112attached to the base substrate 120. The embodiment of the presentinvention discloses the manufacturing process of the DMD packages, onwhich a single semiconductor chip 112 is mounted on the base substrate120. However, it still falls within the spirit and scope of the presentinvention that a plurality of the semiconductor chips 112 are mounted onthe base substrate 120 in rows, and multiple packages are simultaneouslymanufactured. In such case, the photoresist 113 formed on a plurality ofthe semiconductor chips 112 are collectively removed.

[0061] As shown in FIG. 15, the components including the semiconductorchip 112 are hermetically sealed (step 198). In order to protect thesemiconductor chip 112 on the base substrate 120 and the bonding wire140 from the external environment, the semiconductor chip 112 and thebonding wire 140 are hermetically sealed. A window lid 150 is attachedto a metal sealing ring 124 on the periphery of the base substrate 120by thermo-compression, and thereby the cavity (129 in FIG. 4) containingthe semiconductor chip 112 is hermetically sealed.

[0062] The window lid 150 comprises a metal lid frame 152 in contactwith the metal sealing ring 124, and a window 154 perforating the metallid frame 152 on the center. A reflectance coating film 156 is formed onthe lower surface of the window 154 on its periphery, and a moisturegetter 158 is attached to a lower surface of the metal lid frame 152.

[0063] In order to prevent the bonding wires 140 from contacting thelower surface of the window lid 150 attached to the metal sealing ring124, it is preferable that a distance between the upper surface of thebase substrate 120 and the lower surface of the window lid 150 isgreater than the height of the bonding wire.

[0064] When the metal lid frame 152 is attached to the metal sealingring 124 by thermo-compression, a portion of the metal lid frame 152attached to the metal sealing ring 124 has a thickness less than thethickness of the other portion of the metal lid frame 152. This allowsthe effective heat transfer from a thermo-compression means through theupper surface of the metal lid frame 152. An adhesive means having alower melting point than that of the above-described metal adhesive 130is used between the metal sealing ring 124 and the metal lid frame 152.This prevents the conventional deformation problem that results fromre-melting the metal adhesive 130.

[0065] As shown in FIG. 16, the heat sink stud 160 is attached (step199). In order to effectively draw heat away from heat-generatingsemiconductor chip 112, the heat sink stud 160 is attached to the lowersurface 123 of the base substrate below the semiconductor chip 112. Themanufacture of the improved DMD package 200 is complete.

[0066] Accordingly, in the manufacturing process of the presentinvention, since the photoresist is not removed immediately after theseparation of the wafer into individual semiconductor chips, but isremoved after the wire-bonding step, the present invention simplifiesthe manufacturing process of the DMD packages as follows:

[0067] First, since the wafer is sawed by the full-cutting method, thepresent invention thus reduces the number of steps required forindividual semiconductor chip 112 singulation. Second, because themirrors 116 of the semiconductor chip 112 are protected with thephotoresist 113, the present invention can omit the conventional step offorming the first anti-sticking film. The present invention also omitsthe conventional step of removing undesirable organic particulate orcompounds after the wire-bonding step. During the step for removing thephotoresist, the present invention also removes any the organiccompounds remaining on the upper surface of the base substrate, thesemiconductor chip and the bonding wire.

[0068] In the present invention, the mirrors 116 of the semiconductorchip 112 are protected by the photoresist 113. Therefore, instead of theAg-epoxy adhesive, a metal having a low melting point such as a soldercan be used in the chip-attaching step. Although the chip attaching stepis carried out at high temperatures, the mirrors 116 formed with thephotoresist thereon thus are prevented from high temperature damage(e.g. deformation) that may otherwise occur. Accordingly, the presentinvention solves the affixation and out-gassing problems described aboveinvolving a metal adhesive with a low melting point and an Ag-epoxyadhesive (relating to the hygroscopicity of the Ag-epoxy adhesive andthe exhaust gas generated during curing of the Ag-epoxy).

[0069] Further, because the photoresist-removing step is performed withthe semiconductor chip being mounted on the base substrate 120, it isvery easy to handle the inverted DMD semiconductor chip 112.

[0070] Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be understood that manyvariations and/or modifications of the basic inventive concepts hereintaught which may appear to those skilled in the art will still fallwithin the spirit and scope of the present invention as defined in theappended claims.

What is claimed is:
 1. A digital micro-mirror device (DMD) packages,comprising: a base substrate having a top surface and a bottom surface;a metallic layer formed on the top surface of the base substrate; ametallic adhesive formed on the metallic layer; a semiconductor chipmounted on the metallic adhesive, the base substrate electricallyconnected with the semiconductor chip; one or more mirrors mounted onthe semiconductor chip; a hermetic sealing means covering thesemiconductor chip including the one more mirrors.
 2. The DMD package ofclaim 1, which further comprises a heat sink attached on the bottomsurface of the base substrate.